The invention relates to an apparatus and method for implanting an intramedullary rod for fixation of a fracture in a long bone such as the femur, and particularly, to an apparatus and method for detecting the location of the distal screw holes in such an intramedullary rod for locking the rod in place.
A severe fracture in a long bone such as a femur or tibia, tends to cause the fractured bone segments to compress, shortening the length of the bone. A traditional treatment is to use an intramedullary rod inserted into an opening made in one end of the bone and affixed to the bone segments. The intramedullary rod substantially occupies the medullary canal, and must be affixed or locked to the bone segments on each side of the fracture to prevent shortening or rotation of the bone. One problem in the locked intramedullary rod technique is locating the distal hole(s) in the distal end of the rod and successfully aligning transverse screws with the hole(s) for insertion through the bone wall. One known technique for locating a distal hole is an X-ray imaging technique that utilizes a free hand technique. The image intensifier (fluoroscope) is interactively repositioned until an accurate circular image of the rod hole is produced. This occurs when the image intensifier is located on the center line of the hole. The insertion point for the transverse screws may then be determined. The problem with this technique is the exposure of the patient and the operating team to X-radiation which can be excessive if the procedure to properly locate the distal holes results in a large number of attempts. In particular, the hands may be excessively exposed to the X-radiation. Even if protective gloves and clothing are utilized, the effects of excessive exposure to X-radiation are not entirely eliminated. In addition, if correct alignment is not obtained, multiple perforations of the bone may occur.
Other techniques have been proposed for locating the distal holes in an implanted intramedullary rod which do not require X-ray imaging techniques. For example, U.S. Pat. No. 4,881,535 discloses a mechanical jig that is accurately retained in relationship to the rod by a portion extending into the bone through the opening made in the proximal end of the bone. The jig includes an external portion that extends parallel to the bone for aligning screws with the apertures in the rod provided along the externally extended portion of the jig. This technique may be successful, however, there is an opportunity for relative movement between the jig and the rod which may result in misalignment. U.S. Pat. No. 4,877,019 discloses an electrical probe which may be inserted into a hollow interior of an intramedullary rod for generating an electrical field which may be detected through the distal intramedullary holes. An oscilloscope signal may be utilized to visibly display the alignment of the distal holes. U.S. Pat. No. 4,621,628 discloses a similar technique wherein an electrical probe inserted in the hollow interior of an intramedullary rod detects an axially symmetrical field generated by at least one magnet on the outside of the bone. The successful use of devices using electronic imaging depends upon qualified operators of the electronic equipment and proper functioning of the equipment. The imaging techniques are relatively complex and require additional electronic equipment and visual displays in the operation area. The costs of the techniques in terms of the task accomplished also is a consideration which may weigh against their success and use.
Accordingly, an object of this invention is to provide a simple yet reliable apparatus and method for locating the distal holes in an implanted intramedullary rod so that screws can be inserted through the bone and rod to transfix the rod at the distal femur.
Another object of the invention is to provide an apparatus and method for implanting and transfixing an intramedullary rod within the intramedullary canal of a long bone which is simple and does not require the use of electronic equipment.
Another object of the invention is to provide an apparatus and method for implanting an intramedullary rod and locating the distal holes in the rod using high-energy magnets for accurate alignment of the distal holes and screws for insertion through the bone.